Enemy Mine
by SilveryMoon34
Summary: One shot based on the lovely nasty-bones's AU Underclass. UT!Sans and US!Pap. Flirty, nerdy little twink Sans, jealous Pap, Chara's advice accidentally gets their arch nemesis laaaaaaaaid. Porn with very little plot. Read at your own risk.


**A/N: inspired by nasty-bones's lovely AU, Underclass, and a few pictures they drew for it. Pap and Sans are not brothers in this AU, just classmates, but I'm putting it under fontcest anyway. Please enjoy my first foray into skeleton sin.**

 **Enemy Mine**

Someone came in-attracted by his crying, no doubt-but not the monster he so desperately wanted to see. He sunk low in his vandalized seat, swiping harshly at his eye sockets.

"Chara. Come to add some more shit to the pile?"

The red-eyed teenager blinked, mouth clicking shut on whatever they'd been about to say. They glanced down at Sans's desk, surprise twisting into disgust.

"Ugh. Sansy Sans, you know me. If I wanted to mess with you, I'd do it to your face. I'm an asshole, sure, but I've got standards, standards much higher than this middle school bullshit." They plopped into the seat in front of Sans, backwards. He cringed, wishing they'd just go away.

"Seriously, ew. This is so bad, I'm actually offended on principle. 'Suck my dick'? 'Faggot'? I could shit better insults. For chrissake, it's not even _spelled_ right!"

"I noticed. Point made. Could you...go away now?" Sans hated how weak and sniffly his voice sounded.

Chara went on, as if he hadn't said a word. "Tell you what, in light of this abomination, I'm gonna be your fairy frickin' godmother and give you a piece of advice."

A small, shaky laugh tore, unbidden, out of Sans's throat. "Give me advice? _You?_ Why?"

"I'm feelin' sentimental. Besides, these shitstains are an embarrassment to bullies everywhere. Enemy of my enemy, yada yada. Shut up and pay attention."

Truly curious now, Sans wiped his eye sockets one last time, and listened.

"Take it from a real bully: they're only doing this because they know they can make you cry at the drop of a hat. Full offense, nerdo, you're an easy target. Small and squishy, no friends? Picking on you is as easy as kicking a three legged puppy. So, you know what you gotta do?"

"What?"

"Act like it doesn't bother you. Better yet, _own it._ Insults? Smile like Mettaton does when his fangirls call him hot. They call you a faggot, a crybaby? Blow 'em a kiss." Chara cackled, caught up in their own deviousness. "No, serious, blow 'em a kiss. Have you _seen_ a homophobe's _face_ when a gay man acts flirty at 'em? Hil-aaar-ious."

Sans recoiled, as if Chara had just smacked him in the face with something gross and possibly dead. "No! Are you crazy? I c-can't do that! That'll just make everything so much worse!"

"Dude." Chara spread their arms, framing the crude 'artwork' scratched into his desk. "You're already _at_ worse."

Sans kept shaking his head, unable to wrap his mind around the idea that _Chara_ , of all people, was throwing him an idea that not only made a crazy sort of sense, but also didn't involve mayhem of any kind. Of their usual variety, anyway.

"B-But I'm not-"

"Not what? Gay? Puh-lease. The entire universe has seen the way you look at that idiot jock Papyrus. You're gayer than a sports anime for him. Anyway, are or not, doesn't matter. Knock 'em off their high horses-" Chara's eyes flashed, dark red turning crimson, "-then _annihilate them_."

And there it is. "But I don't _want_ to annihilate anybody. I just want all this to _stop_."

Chara made a face. "If you wanna be boring about it, fine. Either way, you can keep rolling over and taking their shit like a little nerdy bitch, or you can get up and get some shots in yourself before _worse_ becomes _worst._ Up to you." Having said their piece, Chara hopped up, weirdly graceful for a homicidal creep, and strolled out of the classroom, whistling, not a care in the world.

It made sense. But could he do it? He felt his face burn and his anxiety spike just thinking about it.

He got up, shoving it all from his head, for now wanting nothing more than a hot shower and his soft bed.

He'd figure everything out tomorrow. Hopefully.

The next morning, 'worse' hit full force. Normally, all he had to endure was some laughter, a few jeers and taunts here and there. Now, with those damning scratches on his desk, he got crude remarks, parroting the words written there as if they were the pinnacle of wit, mimed blowjobs... And it kept going, even after the teacher called the class to order, albeit quieter. Sans felt his sockets prickling with tears again, humiliated, wishing he could just melt or dust right here and be done with it.

Chara's words flashed through his overheated brain.

Could he do it?

It could hardly be worse than this, right?

A small knot of jerks in the back corner of the class were causing the most ruckus-they'd stepped up to take Chara's place as his tormentors this year. Just...something small? Test the waters?

Before he could lose his nerve, he turned. Once he had their full attention-made clear by the low hoots and more exaggerated blowjob noises-he did it. He gave his best, flirtiest wink, before jerking back to face front, face on fire.

The reaction was instantaneous.

"Did...Did he just _wink_ at us?"

"Ew. Stars, I need a shower now."

But it worked. It shut them up for the rest of the period.

Something bright burned inside of Sans, easing his anxiety, his fear. It felt like finally, _finally_ he had an edge, a weapon even his thin bony arms could use. Maybe it would get worse, maybe it wouldn't, but at least now he was fighting back-if only in a small way.

Next period, they regrouped and hit back hard, even getting a smaller group of girls to join in.

Faggot. Cocksucker. Twink. Bitch. Sans didn't hesitate this time, turning smoothly on his heel with a triple threat: finger gun (one handed, because books) mile-wide grin, a wink. Stars, Chara was _right_ -the looks of surprise and sheer horror on their faces were _priceless_. And to make it even better, for once the oohs around the room weren't directed at him. The grin on his face as he took his seat was completely genuine; he even sat up straighter, uncowed.

They didn't wait until next period to start again, visibly furious now that Sans remained unmoved. Unbroken. Feeling extra bold, he blew both groups a kiss as he pretty much skipped out of the room, first for once.

In hindsight, he realized he got pretty carried away, nonverbally flirting at anyone who bothered him with so much as a nasty look. But lunch was where things got...embarrassing.

He could hear them behind him-unable to break him to his face, they resorted to whispers. As he grabbed a spoon, a devious thought occurred to him.

He scooped up some orange jell-o, and, walking backwards, he made eye contact...and deliberately licked it off as lewdly as possible with his conjured tongue, even making a soft, breathy little noise-

"Uh, Sans?"

He froze, spoon clattering back on his plate.

"What are you doing?"

"Nothing!" He turned quickly, nearly bumping into the familiar lanky form behind him. "Uh, hi, Pa-uh, I mean, what, idiot?"

Papyrus glanced down at him, then back at his would be tormentors. "Are they bothering you?"

"Who bothering what?" Ohh stars, he couldn't think straight, his so-called big brain just a ball of flustered mush. Papyrus saw him...doing _that_...at a bunch of strangers. He must think he's some gross slut now-

Pap gave him one of his slow, sweet smiles, the very thing that made him fall stupidly in love with the big idiot in the first place. "Good!" He snatched Sans's glasses off his face, holding them up above their heads. "Because that's _my_ job."

"Paaaaaaap!" Sans whined. "Give those back! You're gonna make 'em all gross and smudgy with your dirty Neanderthal hands!"

Really, it was just part of the game. Sans wasn't really worried-Pap always treated his glasses with the utmost care. And...he didn't actually think Pap's hands were anything like a Neanderthal. They were actually quite nice, long and slender but very strong. He often wondered what they'd feel like, touching-

He jerked away from that train of thought, eye lights going out for a second, his cheeks...and something lower and much more embarrassing...flushing again.

"Make me, short stack," Papyrus purred, completely unaware.

Sans pouted up at him. "Come _on_ Papy. I haven't got all lunch period and I'm _hungry_."

"Fiiiiiine." Papyrus unfolded the glasses, perching them back on Sans's face carefully, his lovely fingers gently brushing the sides of his skull.

His heart fluttered at even that simple touch. Yeah. Gay as a sports anime for this big idiot. No doubt about it.

His heart sunk, as it always did, when their brief encounter ended and Pap had to go back to his friends. Sans kept a straight face though, walking to his favorite corner of the courtyard. Technically, students weren't allowed to eat there, but being a teacher's pet had its perks. No one bothered him.

He kept up with Chara's advice, but it had lost its thrill of victory. All he could imagine now was Papyrus and his ever gentle hands. Heh, yeah, like _that_ could ever happen. Papyrus was sweet, brave, popular; _he_ was just a short nerd resorting to slutty tricks to get bullies to back off. Resorting to the advice of the very homicidal dirtbag who made his life a living hell the two years prior. If there was ever a sign of desperation, that was it. Pap could do better.

At the end of the day, he opened his locker with a sigh, all too ready for home.

"Hey, homo."

Sans turned around, rallying his last bit of energy-he nearly dropped his books. It wasn't a small group anymore; they surrounded his locker in the now very empty hallway, blocking every exit.

Using his last spurt of bravery, he tried. "What's up, hot stuff?" His voice shook, completely unconvincing. The speaker glared, cocking a fist back-

And suddenly Papyrus was there, grabbing the other monster's fist, spinning him around and shoving him into the monster next to him. Sans's face fell with the monster when Papyrus turned to him, not with his honey smile but with a flat, dark, stormy glare.

 _Oh stars, this is it. He hates me._ "P-Pap-?" Sans barely got the word out before he was shoved against the lockers...and kissed. Deep, rough, possessive; it made Sans's legs quiver but no longer in fear. Stars, it was...h-hot. Doing things to him he didn't think were possible.

Pap broke the kiss, smiling down at Sans now but still different from his old one-honey with an edge.

"Sans?" he hummed, still with that deadly smile. Still close enough to make it difficult to breathe, in the best way. Sans's soul hammered in his chest, starting to glow.

"P-Papy?"

"You're mine," he purred. No question. No doubt. All of Sans's doubts and insecurities melted away, not a single thought of denying that simple fact in his head. Even if one showed up, it would be false. He'd been Papyrus's the second the other smiled at him for the first time. He touched the hand still pressed against his chest.

"Yes," he breathed.

For a second, Papyrus's dark smile softened, becoming more familiar. Then Sans was in the air, held firmly in Pap's arms as he spun to face his tormentors.

"Listen up, little shits, 'cause I'm only gonna say this once." Sans shivered, feeling the growl rumbling out of Papyrus's chest against his shoulder. He hugged Pap's neck, all out of courage, content to hide in Pap's warmth. "This one is _mine_. Touch him in any way, hurt him in any way, or even _look_ at him the wrong fucking way, and I will end you faster than you can cry for your mommies. Understand? Now back. The fuck. Off."

Sans didn't look, but the resounding thud and squeaks of running feet told him Papyrus's threat had been extremely effective.

"Pap-" he lost his breath for a second at the sudden shift of air. He looked up, flushing as he realized where Pap had teleported them to.

Papyrus dropped him on his bed, stepping in between Sans's accidentally spread legs. He leaned over, kissing him hard again.

"Mine," he purred. Then he surprised Sans by catching his hand, pressing a gentler kiss into his palm. "Mine." Wrist. Arm. "Mine." He let go, sliding both hands under Sans's sweater, running his fingers over sensitive ribs.

Sans gasped, arching into his touch. "Yours," he breathed. "Yours, you big beautiful idiot."

Pap hummed in approval, pushing Sans's sweater up and over his head. He smiled his old smile at the bright glow under Sans's ribs, as vivid as the one that painted his cheeks. "Ready?"

Too overwhelmed to speak, Sans nodded.

Papyrus slipped a hand under the waistband of Sans's uniform slacks, finding that he'd already created an opening for him, all nice and slick, like a good boy.

"That doesn't seem comfortable. Let me help with that." He pulled Sans's slacks completely off. "Mmm, so cute." He stripped off his own jacket, pulling his slacks down enough to free his erection.

Sans whined softly at the sight, opening his legs further. Pap wasted no time obliging him, easing himself into the welcoming warmth with a quiet groan.

Sans panted, pulling Pap down by his tie for another hot kiss, locking his legs around Pap's hips.

So...deep. He was already seeing stars, and Papyrus hadn't even started thrusting yet.

Once seated fully inside him, Papyrus smiled his sweet smile, stroking Sans's cute little flushed face. Sans nuzzled his hand, full to bursting with affection.

Then Pap started to move, and affection caught fire, turning to pure, unashamed lust. He didn't stop his noises, too caught up in what Papy was doing to him to care.

Pap kept kissing him, holding his hips as he drove into him again and again. "So...tight. So good," he gasped between kisses. "Good boy. Good, Sans."

It was almost guaranteed neither would last long.

Pap hit a point deep inside him, sending an electric shock of pleasure through him.

"Yes...there... _Please_ ," he babbled, hanging on for dear life. Three good thrusts on that spot and he was gone, whole body locking up in his first earth-shattering orgasm. With Sans tightening up around him, Pap followed not long after.

Pap buried his face in Sans's neck, both riding out the aftershocks. Sans stroked Papyrus's spine, basking in the afterglow of being well and truly fucked.

"Mine," he giggled.

"Obviously." Papy sat up, laying a soft kiss on Sans's jaw as he eased out of him. Sans clung to his neck; Pap chuckled, pulling the tiny, sated nerd to him as he rolled over, tugging his blankets over them both.

"Love you," he sighed, nuzzling the precious skull.

"Love you too, Papy," Sans yawned, hugging tighter.

Maybe he should take the advice of a homicidal maniac more often.

 **A/N: And fin. Bonus cookie for those of you who spotted the Easy A reference. Hope you enjoyed!**


End file.
